Simulation on Kink-Band Formation Based On X-Ray Computed Tomography Modeling

Kink-band failure is a representative failure mode of a unidirectional carbon fiber reinforced plastics (CFRP) under axial compressive loading. Unidirectional CFRP has initial fiber waviness, and it may trigger kink-band failure. However, initiation of kink-band is not clarified yet. In this paper, three-dimensional finite element model with an actual fiber waviness was constructed by means of X-ray computed tomography (XCT) imaging. Simulation on compression was carried out using the three-dimensional model. A small unidirectional CFRP cylinder was fabricated and scanned the internal fiber structure using an XCT system. The three-dimensional model of the unidirectional CFRP was developed from the XCT images by tracking each fiber positions along the longitudinal direction. Numerical simulation on compression was performed using the constructed three-dimensional finite element model. With increase of compressive loading, matrix deformation was increased locally at some volumes inside the unidirectional CFRP due to fiber random waviness. Matrix started to yield at the volumes, which was considered as an initiation of kink-band formation. The applied compressive load started to decrease after the matrix yielded showing snap-through behavior in the load-displacement relation. The yielded volume of the matrix expanded through the cross-section with rotation of carbon fibers, and kinkband was gradually formed. The numerical simulation revealed initiation and formation of kink-band in a unidirectional CFRP by the random fiber waviness model.